When the old pro finally caught up, the 21-year-old youngster flinched.

As Blaney attempted to pass a slower car in the back straightaway Saturday on the final laps, Blaney’s car wiggled, Busch ducked inside, raced past and held on to win the Xfinity Series race at Indianapolis for the second time in three years.

The 0.421-second victory margin was the closest of the four races held on Indianapolis’ historic 2.5- mile-oval. Rookie Daniel Suarez of Mexico finished third.

“It’s cool and it’s great and all, and made for an exciting last lap,” Busch said. “We just never should have been in that position to begin with. If it wasn’t for a mistake by the car in front of us, we would have lost today.”

Instead, it was yet another stunning chapter in Busch’s remarkable comeback.

Since missing the first three months of the season after breaking his right leg and left foot in the Xfinity opener at Daytona, the 30-year-old Cup regular has reached victory lane five times — twice on the Xfinity circuit and three in the Sprint Cup Series. He also won the pole Saturday, his third straight at Indy, and has won two of NASCAR’s last three undercard races here.

But Busch had to sweat this one out.

“I’m still kind of warm. I’m not even cool in here yet and I’m soaking wet,” he said after extending his career wins record to 72. “I just have to get dry and get some fluids in me tonight, take it easy and get ready for tomorrow.”

Blaney, meanwhile, was distraught.

After Busch took the outside line on the final restart of the race, Blaney outraced Busch into the first turn, took the lead on Lap 76 and held it — until he encountered the slower car of Derrick Cope.

Blaney moved toward the wall with Busch near his tail end. That forced Blaney’s car to bobble and gave Busch the chance to slip inside.

“Not many can say they had a chance to win at the Brickyard and gave it away,” Blaney said. “But I did just that, so I think I’m the only one in that category. So I’m leading that category. That’s definitely going to sting for a long time.”

How bad was it?

After the race, Blaney referred to himself as a “bad driver’ and said the mistake would go down as a “laughingstock” for a long time.

Neither Blaney nor Busch can allow Saturday’s results to linger.

Both are scheduled to start Sunday’s Brickyard 400.

While Blaney acknowledged it won’t be easy to get over Saturday’s close call, Busch may have an even more difficult challenge — getting back to 100 percent overnight. But celebrating another win will help.

“Fortunately there on that long run, I was behind Blaney and I was faster than he was, I could keep up with him, I could draft on him a little bit,” he said. “It’s real tough to time, and there really was no timing on that. With that kind of run, there’s no blocking that kind of run. It didn’t matter what he was going to do.”